29 research outputs found
Analysing multiparticle quantum states
The analysis of multiparticle quantum states is a central problem in quantum
information processing. This task poses several challenges for experimenters
and theoreticians. We give an overview over current problems and possible
solutions concerning systematic errors of quantum devices, the reconstruction
of quantum states, and the analysis of correlations and complexity in
multiparticle density matrices.Comment: 20 pages, 4 figures, prepared for proceedings of the "Quantum
[Un]speakables II" conference (Vienna, 2014
An Elementary Quantum Network of Single Atoms in Optical Cavities
Quantum networks are distributed quantum many-body systems with tailored
topology and controlled information exchange. They are the backbone of
distributed quantum computing architectures and quantum communication. Here we
present a prototype of such a quantum network based on single atoms embedded in
optical cavities. We show that atom-cavity systems form universal nodes capable
of sending, receiving, storing and releasing photonic quantum information.
Quantum connectivity between nodes is achieved in the conceptually most
fundamental way: by the coherent exchange of a single photon. We demonstrate
the faithful transfer of an atomic quantum state and the creation of
entanglement between two identical nodes in independent laboratories. The
created nonlocal state is manipulated by local qubit rotation. This efficient
cavity-based approach to quantum networking is particularly promising as it
offers a clear perspective for scalability, thus paving the way towards
large-scale quantum networks and their applications.Comment: 8 pages, 5 figure
Integration of Hi-C with short and long-read genome sequencing reveals the structure of germline rearranged genomes
Structural variants are a common cause of disease and contribute to a large extent to inter-individual variability, but their detection and interpretation remain a challenge. Here, we investigate 11 individuals with complex genomic rearrangements including germline chromothripsis by combining short- and long-read genome sequencing (GS) with Hi-C. Large-scale genomic rearrangements are identified in Hi-C interaction maps, allowing for an independent assessment of breakpoint calls derived from the GS methods, resulting in >300 genomic junctions. Based on a comprehensive breakpoint detection and Hi-C, we achieve a reconstruction of whole rearranged chromosomes. Integrating information on the three-dimensional organization of chromatin, we observe that breakpoints occur more frequently than expected in lamina-associated domains (LADs) and that a majority reshuffle topologically associating domains (TADs). By applying phased RNA-seq, we observe an enrichment of genes showing allelic imbalanced expression (AIG) within 100 kb around the breakpoints. Interestingly, the AIGs hit by a breakpoint (19/22) display both up- and downregulation, thereby suggesting different mechanisms at play, such as gene disruption and rearrangements of regulatory information. However, the majority of interpretable genes located 200 kb around a breakpoint do not show significant expression changes. Thus, there is an overall robustness in the genome towards large-scale chromosome rearrangements
Integration of Hi-C with short and long-read genome sequencing reveals the structure of germline rearranged genomes
Here the authors characterize structural variations (SVs) in a cohort of individuals with complex genomic rearrangements, identifying breakpoints by employing short- and long-read genome sequencing and investigate their impact on gene expression and the three-dimensional chromatin architecture. They find breakpoints are enriched in inactive regions and can result in chromatin domain fusions.Structural variants are a common cause of disease and contribute to a large extent to inter-individual variability, but their detection and interpretation remain a challenge. Here, we investigate 11 individuals with complex genomic rearrangements including germline chromothripsis by combining short- and long-read genome sequencing (GS) with Hi-C. Large-scale genomic rearrangements are identified in Hi-C interaction maps, allowing for an independent assessment of breakpoint calls derived from the GS methods, resulting in >300 genomic junctions. Based on a comprehensive breakpoint detection and Hi-C, we achieve a reconstruction of whole rearranged chromosomes. Integrating information on the three-dimensional organization of chromatin, we observe that breakpoints occur more frequently than expected in lamina-associated domains (LADs) and that a majority reshuffle topologically associating domains (TADs). By applying phased RNA-seq, we observe an enrichment of genes showing allelic imbalanced expression (AIG) within 100 kb around the breakpoints. Interestingly, the AIGs hit by a breakpoint (19/22) display both up- and downregulation, thereby suggesting different mechanisms at play, such as gene disruption and rearrangements of regulatory information. However, the majority of interpretable genes located 200 kb around a breakpoint do not show significant expression changes. Thus, there is an overall robustness in the genome towards large-scale chromosome rearrangements
Negative Refraction in Atomic Two-Component Media
Negative Refraction in Atomic Two-ComponentMedia: In the present thesis we study the feasibility of negative refraction at optical wavelengths and low absorption in gases consisting of two species of atoms. Compared to a single-component system, we expect it to be easier to find candidates for an experimental realization due to less stringent conditions that must be met. The two involved species contribute the electric and the magnetic response, respectively. To obtain a negative refractive index, both responses must be large. Therefore, we optimize the magnetic susceptibility, which typically is considerably smaller than the electric susceptibility, in different systems. Moreover, we investigate a mechanism in so-called closed-loop systems that enhances the magnetic response by a factor of 1, the inverse fine structure constant. Closed-loop configurations are characterized by the fact that the coupling control and probe fields build up a closed interaction loop in the level scheme. We find that the enhancement occurs, as the electric probe field component scatters into the magnetic probe transition. Using the previous results, we calculate the refractive index for several combinations of two realistic level schemes and address the occurring instabilities of the probe field. We obtain a refractive index of n = 6.4 and n = 3.7, respectively, at vanishing absorption for two different systems
Parametric and nonparametric magnetic response enhancement via electrically induced magnetic moments
The realization of negative refraction in atomic gases requires a strong
magnetic response of the atoms. Current proposals for such systems achieve an
enhancement of the magnetic response by a suitable laser field configuration,
but still rely on high gas densities. Thus further progress is desirable, and
this requires an understanding of the precise mechanism for the enhancement.
Therefore, here we study the magnetic and electric response to a probe field
interacting with three-level atoms in ladder configuration. In our first model,
the three transitions are driven by a control field and the electric and
magnetic component of the probe field, giving rise to a closed interaction
loop. In a reference model, the coherent driving is replaced by an incoherent
pump field. A time-dependent analysis of the closed-loop system enables us to
identify the different contributions to the medium response. A comparison with
the reference system then allows one to identify the physical mechanism that
leads to the enhancement. It is found that the enhancement occurs at so-called
multiphoton resonance by a scattering of the coupling field and the electric
probe field mode into the magnetic probe field mode. Based on these results,
conditions for the enhancement are discussed.Comment: 12 pages, 8 figure